Game settings

There are two basic ways to play: with or without your memory.
If you choose to play without your memory, then it is what it sounds like: you'll be born into the world knowing nothing.  Now, when you exit the world, you will retain all your memories from the game and you will also regain your real memories.  Think of it as if your real memories are in a sealed bunker during game play.  The only way to open that sealed bunker is to die in the game.  Now, you won't know that during game play.  You won't know anything outside of the game.  The game, in all likelihood, will appear to you as real life.
If you choose to play with your memory, then you retain all your previous memories from both real life and any other games you have played previously.  You may not be able to realize all this knowledge when you are born into the game, but you will still be in possession of the knowledge.
There are other options you can set before entering the game in regards to memory.  You can choose for all the other people in the game to be born with no prior knowledge, with some knowledge or with full knowledge.  This translates roughly to the lack of knowledge of a standard human baby, some patchy knowledge of prior game play or full knowledge of several bouts of game play.  You can also adjust this setting so that a few people have full knowledge while most have none.  The options are fully customizable with three categories: what percentage of the population of the game world have no knowledge, what percentage have patchy knowledge and what percentage have full knowledge.
With these two basic gameplay options, you can see that vastly different game worlds are yours to explore!